What two handed stance are you using? Are you sure you are using your dominant eye for both stances? If you are using an offhand stance and using your right hand and right eye or left hand and left eye, you are "forcing" one eye to be dominant. On rare occasions, there is no perceivable eye dominance. Are you applying "Kentucky windage or chasing the holes around the target?"
Have you established your natural point of aim for either stance? In order to do that, perform the following exercise. With you gun empty, assume your stance, get a good sight picture. Now, without lowering the gun, close your eyes, lower the gun, move your head 60 or 70 degrees to the left or right. Now, without opening your eyes, raise your gun to a point where you think your sights will be on the target. If you are off left or right by a substantial margin, shuffle your feet until you get a good sight picture. Do not move your upper body. Your upper body is already "comfortable" with the stance. So, you adjust by moving your entire body. If you are off in elevation, move your arms to acquire a good sight picture. Practice that until you can, without a lot of concentration, acquire your stance, raise your gun and be on target with little or no adjustment. When you make ready to shoot, don't look at your gun until it's raised to the point of aim: look at your target and then bring the gun up to your eye level. That way, you don't hunch your shoulders and move the parallel line from your eye, through the sights to the target. Concentrate on your front sight. The sequence in acquiring the target should be, target, rear sight, front sight target. When those steps are complete you should have a focus on the front sight. Rear sight and target should be slightly out of focus. If you lose the front sight, you will miss the target. The front sight is the most important component in the entire geometry.
What I would do is use a sitting supported stance, the upper body in an Isosceles form and pick a spot on the target and shoot for that spot every time regardless of hitting or not hitting the bullseye. Establish once and for all your eye dominance. There are several exercised you can do. Make sure you are using good trigger control, and proper follow through. If you are using a Weaver or modified Weaver, go to an Isosceles. the Isosceles will give you the most stable standing stance. Start at about 10 feet from the target and gradually move back to the 7 yards. In your follow through, just go to the trigger reset and don't take your finger off the trigger. Don't look up after every shot. Two universal truths to shooting: 1) once the round leaves the muzzle nothing you do will change the impact point. Before the round leaves the muzzle, everything you do will change the impact point.
Hope this helps a little.
